1. Field of the Invention
This invention relates to a motor apparatus for reducing the vibration of a motor, and particularly to a motor apparatus suitable for an image reading apparatus or the like.
2. Related Background Art
In an image reading apparatus used in a copying machine or the like, a stepping motor has heretofore been used because highly accurate positioning of a movable member is required. To drive the movable member of the image reading apparatus at a high speed with low vibration by the stepping motor, the acceleration and deceleration of the motor are requisite.
Also, to read color information, reading at a constant speed, free of vibration, is necessary and therefore, it is popular in the design of the apparatus to provide an approach run distance required until the vibration created after the acceleration becomes null.
Also, regarding the vibration in the constant speed portion of the motor rotation, the motor becomes a vibration source due to a torque ripple conforming to a step angle and the thin lines of an image become jaggy. To combat this problem, it is possible to use a magnet damper that does not add to the inertia to the motor shaft during the aforementioned acceleration operation, but adds to the inertia to the motor shaft when it is moving at a constant speed for the reason set forth later, to thereby smooth the rotation between step angles, and it is possible to reduce the vibration.
It is also possible to fractionate the step angle of the motor to thereby reduce the torque ripple and reduce the vibration.
However, the number of images read by the image reading apparatus per unit time has become higher year by year and therefore, it has become impossible to secure a sufficient approach run distance. Also, when the inertia working during acceleration is added to the motor shaft, the acceleration time increases and a higher speed becomes impossible and a very great inertia could not be given. Therefore, the vibration components of the distal end of a read image have become large and the distal end of the read image becomes jaggy, and this has caused a great reduction in the quality of the image.
The reason set forth above has become a factor for greatly reducing the quality of the produced image by being jaggy or a factor for hindering the downsizing of the apparatus by the increase in the approach run distance resulting from a higher reading speed.
The present invention has been made in view of the above-noted situation and an object thereof is to provide a motor apparatus reduced in vibration caused during acceleration and during operation at a constant speed.
Another object of the present invention is to mount two damper means on a motor drive shaft to thereby reduce vibration caused during the driving of the motor.
Still another object of the present invention is to use a magnet damper as a first damper means and use a rubber damper as a second damper means.
Yet still another object of the present invention is to use a magnet damper and a rubber damper to shorten the reading time of an image to thereby increase the speed of the apparatus.